US20170037524A1

US20170037524A1 - Reactor Having a Sacrificial Anode

Info

Publication number: US20170037524A1
Application number: US15/228,816
Authority: US
Inventors: Siegfried Egner; Iosif Mariakakis; Uwe Claussnitzer
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 2015-08-06
Filing date: 2016-08-04
Publication date: 2017-02-09
Also published as: EP3127871B1; ES2927957T3; EP3127871A1; DE102015215037B4; DE102015215037A1; CA2938400A1

Abstract

A reactor is proposed that comprises a cathode and a sacrificial anode, in which a spacing between cathode and anode is kept constant by the cathode following, or tracking, the anode.

Description

Reactors that have a cathode and an anode are often used in process technology. In the operation of the reactor, an electrical voltage is applied between the cathode and anode such that the anode is consumed (sacrificial anode).
DE 10 2010 050 691 B3 and DE 10 2010 050 692 B3 describe a method and a reactor for recovery of phosphate salts from a liquid, where the sacrificial electrodes consist of a magnesium-containing material. The invention is based on the task of making available a reactor that comprises a cathode and an anode (sacrificial anode) that ensures better process conduct and consequently better results with minimized electricity consumption and optimum utilization of the material of the sacrificial anode at the same time. In addition, the operating cost should be minimized.
This task is solved according to the invention by a reactor comprising a housing, a cathode, and an anode, where the cathode and the anode delimit a channel and where the cathode can be moved in the housing relative to the anode.
In this way, a distance between the cathode and anode is always constant independent of the consumption of the anode. Consequently, the electrical field between the anode and cathode is always the same and optimum conversion rates are achieved in the reactor with low energy consumption at the same time.
As a rule, it is advantageous if the cathode, which is not consumed, is moved relative to the anode. As a rule, the cathode is made of stainless steel or another corrosion-resistant electrically conductive material. Therefore, it is advantageous to accommodate the cathode such that it can slide in the reactor housing. The desired relative movement between the cathode and the stationary anode arranged in the housing can be brought about in this way. It is of particular importance in conducting the process that the spacing S between the surfaces of the anode and cathode remains constant regardless of the consumption of the anode. These surfaces delimit a channel through which the liquid being treated flows. Thus, if the geometry of the channel and the electrical field that is present between the electrodes (anode and cathode) are constant, specific and very good conversion rates are achieved with minimal energy consumption.
In an advantageous embodiment of the invention, the desired constant spacing S can be achieved by at least one electrically nonconductive spacer, for example one made of plastic, being disposed between the surfaces of the anode and cathode delimiting the channel. As a rule, it is advantageous to provide at least two spacers in order to prevent tilting of the anode and cathode. These spacers are dimensioned so that the spacing S is maintained regardless of the consumption of the anode.
The spacing S can also be kept constant by means of gravity, one or more springs, and/or one or more actuators. If gravity is utilized, for example, to track the cathode to the anode, then arranging the anode below the cathode in the vertical direction is a possibility, so that the cathode is moved in the direction of the anode by the force of gravity. If at least one spacer according to the invention is disposed between the surfaces of the anode and cathode that delimit the channel, then the spacing between the surfaces of the anode and cathode that delimit the channel are always kept constant in a very simple and reliable way, independent of the consumption of the anode.
Of course, it is also possible in principle to arrange the anode above the cathode and to move the anode in the direction of the cathode by means of gravity. Instead of or in support of gravity, the anode or the cathode can be moved with the help of springs, or with the help of actuators, or electrically, pneumatically, or hydraulically, in order to compensate the material loss of the sacrificial anode and to maintain a constant spacing S between the surfaces of the anode and cathode that delimit the channel.
If actuators are used for tracking the cathode, regulation or control of the spacing between anode and cathode can be provided with sensors, which, as a part of the control circuit, register the consumption or the remaining thickness of the anode. Any suitable sensor types that are available on the market could be used.
The spacing S between the surfaces delimiting the channel can be kept constant most easily if the surfaces of the anode and cathode delimiting the channel are planar. It is further particularly advantageous if the surfaces of the cathode and/or anode delimiting the channel are rectangular. Since an unconsumed anode has a certain thickness, the anode has a cubical shape.
In particular, it is advantageous if the outer dimensions (length and width) of the housing of the reactor according to the invention correspond with the dimensions of current transport systems, for example the so-called Euro pallets. Then the lower part, specifically, of the housing can be employed as a reusable transport container for the anodes and can be transported in the existing supply chains at optimal cost. For instance, a plurality of lower parts with anodes can be stacked on top of each other and bound into a stack, which is then transported to or instead of a Euro pallet and brought to the reactor. In doing so, the transport capacity of a truck or freight train can be utilized in the best possible way, so that transport costs are minimized. In addition, it is possible to move the stacked lower parts, which are loaded with the anodes according to the invention, for example, with a forklift or a pallet truck on site, i.e., in a treatment plant, and to insert them into the reactor. In another advantageous embodiment of the invention, it is provided that the surfaces of the cathode delimiting the channel have a plurality of openings, which act as flushing nozzles. The channel can be cleaned and flushed with a liquid through these nozzles, so that deposits and encrustations that are deposited in the channel during the operation of the reactor can be flushed away.
It is possible to make said opening in the cathode because the cathode is not subject to any wear. However, it is also possible to make these openings in the anode. It is provided in another advantageous embodiment of the invention that the cathode have a distribution chamber, and that the openings are hydraulically linked to the distribution chamber. Then it is possible to simply pump the cleaning liquid under sufficiently high pressure into the distribution chamber. From there, the cleaning fluid passes through the openings into the channel and flushes away any deposits that may be on the surfaces delimiting the channel. The cleaning of the walls delimiting the channel by means of the flushing openings can take place continuously, at fixed intervals, or in dependence on an indicator. Such an indicator, which triggers the cleaning, can be, for example, the current and/or the voltage between the electrodes, or parameters derived from these signals.
To be able to register the process occurring in the reactor and the consumption of the sacrificial anode, means for registering the position of the cathode and/or the anode are provided in the reactor according to the invention. Said means for registering the position of the anode and/or the cathode can be, for example, a position sensor of any design. Said position sensor is advantageously affixed to the electrode that is disposed so that it can move in the reactor housing. In this way, the degree of consumption of the sacrificial anode can be monitored simply and very reliably.
Finally, means are provided for registration of the electrical current that flows between the anode and cathode, and/or the electrical voltage that is applied between the anode and cathode. In this way, the process taking place in the reactor can be monitored simply and reliably. Possible disruptions of the process lead to changes of the electrical current and/or the electrical voltage and thus can easily be detected.
The anode preferably consists of a magnesium-containing material. It can also be more or less pure magnesium. As a rule, the cathode is made of stainless steel, since this material is electrically conductive and will not be attacked by the liquid that is treated in the reactor.
Other advantages and advantageous embodiments of the invention are presented in the following figures.

DRAWINGS

Here:

FIG. 1 shows a lengthwise section through an embodiment example of a reactor according to the invention.

FIGS. 2A, 2B and 2C show three different states of the sacrificial anode.

FIG. 3 shows a plurality of reactors connected in series and in parallel.

DESCRIPTION OF THE EMBODIMENT EXAMPLE

In this embodiment example, the reactor according to the invention consists of a two-part housing with a lower part 1 and an upper part 4. The housing can be separated along a horizontal separation plane in FIG. 1. The contact surface between the lower part 1 and the upper part 4 is indicated with the reference number 21. The separation plane also lies there.
A circumferential seal 23, which can be made, for example, as an O-ring, is disposed in the region of the contact surface 21 so that the liquid inside the housing does not get into the environment.
In order to be able to seal the upper part 4 tightly to the lower part 1 of the reactor, there are additionally closures 8 arranged in the region of the contact surface. By opening the closures 8, the upper part 4 can be separated from the lower part very quickly and with low personnel cost.
In this embodiment example, the lower part 1 accommodates a sacrificial anode 2, which consists of a magnesium-containing material, if the reactor is used, for example, for recovery of phosphate salts from a liquid. One such process is described in the applicant's DE 10 2010 050 691 B3. Using the reactor according to the invention, it is possible, by applying a low electrical DC voltage, to supply magnesium ions to the phosphate- and ammonium-containing liquid and to split the water contained in the liquid into OH⁻and H⁺ions, so that the pH becomes elevated and the reactions needed for precipitation can take place. Through the low energy demand and the omission of the feed of an alkali to raise the pH value, the costs for operating the system are lower than in the process known from the prior art. A pH of about 9 is desirable for the desired precipitation.
Since hydrogen builds up in the operation of the reactor, in the upper part 4, there is a connection 28 through which the hydrogen can be drawn off and sent to another use.
Of course, the anode 2 can also consist of a different material if the process in the reactor according to the invention requires it.
The anode 2 is made as a rectangular plate having a certain thickness; therefore, it is, if all three dimensions are considered, cubical. Frequently, the anode 2 consists of a magnesium-containing material, which must be transported safely and without damage.
This is why provision is made according to the invention to use the lower part 1 at the same time as a reusable transport container for the anode 2. In order to optimize the transport of the lower parts 1, the lower parts 1 preferably have the dimensions of a Euro pallet or another standardized transport container. It is especially preferable if the empty lower parts 1 can be nested. In this way, the transport of the anode 2 from the manufacturer of anode 2 to the user and of the empty lower parts from the user to the manufacturer becomes optimized.
A cathode 3, which as a rule is made of stainless steel, is disposed above the anode 2. The cathode 3 is accommodated in the upper part 4 of the housing so as to be guided in it, such that the cathode 3 moves in the direction of the anode 2 under the effect of gravity.
To keep the cathode 3 from lying directly on the anode 2, spacers 9 are arranged between the anode 2 and the cathode 3. The distance between the surface 25 of the anode 2 and the surface 27 of the cathode 3, which delimit a channel 10, is called the spacing S. A liquid that is being treated in the reactor flows through the channel 10. The spacing S is an important parameter for optimizing the functioning and/or the energy consumption of the reactor. This is why it is very advantageous that the spacing S can be established simply and precisely in correspondence with the requirements of the specific case by means of the spacers 9.
The lateral boundaries (side walls) of channel 10 are not visible in the lengthwise section in FIG. 1. The side walls of the channel 10, which is rectangular in cross section, are formed by the lower part 1 and the upper part 4 of the housing.
In this embodiment example, the surfaces 25 and 27 delimiting the channel 10 are planar. Thus it is extremely simple to keep the spacing S between anode 2 and cathode 3 constant, independent of the consumption of the anode 2.
The upper part of the housing 4 has an inlet 5 and an outlet 6. The liquid to be treated in the reactor is supplied via the inlet 5 and then flows through the channel 10, which is rectangular in cross section, between the anode 2 and the cathode 3 to the outlet 6. The transition regions 31 between the inlet 5 and the channel 10 and between the channel 10 and the outlet 6 are dimensioned very generously.
Of course, it is also possible to provide the inlet 5 and the outlet 6 in the lower part of the housing 1 [sic; lower part 1 of the housing]. Combinations are also possible. If the lower parts 1 are used as transport containers, it is advantageous if there are no connections in the lower part 1, since this simplifies the exchange of lower parts 1 and the anodes 2 in them.
In the operation of the reactor, deposits can form on the surfaces 25 and 27 of channel 10, which will impede the liquid treatment process or even make it impossible. To be able to remove such deposits during the operation of the reactor, a distribution chamber 11 and a plurality of flushing nozzles 12 are made in the cathode 3. The distribution chamber 11 is supplied with a cleaning liquid as necessary via a connection, which is not shown. The cleaning liquid is pumped into the distribution chamber 11 at sufficient pressure and in a sufficient amount and flows through the flushing nozzles 12 into channel 10. Through the number of flushing nozzles 12 and their arrangement and design, in combination with the pressure of the flushing liquid in the distribution chamber 11, it is possible to remove even stubborn deposits on the surface 25 of anode 2, as well as on surface 27 of cathode 3.
The liquid that is to be treated in the reactor can be used as the flushing liquid. In this case, the flushing effect is ultimately achieved through the kinetic energy with which the flushing liquid flows through the flushing nozzles 12 and strikes surface 25. Through the deflection of the flushing liquid at surface 25, the flushing liquid also reaches surface 27 and cleans it.
However, it is also possible to use a flushing liquid containing cleaning additives or chemically active substances.
The anode 2 is electrically contacted, for example, via an electrical contact 14. Correspondingly, cathode 3 is contacted via an electrical contact 15. The electrical connections and the voltage source that supplies the anode 2 and cathode 3 with electric power are not shown in FIG. 1.
As already noted, cathode 3 can drop downward under the force of gravity. This means that with increasing consumption of the anode 2, the cathode 3 will continue to fall farther downward in the direction of the lower housing part 1.
The invention makes use of this effect in that the position of the cathode 3 relative to the upper part 4 of the housing is used as an indicator for the consumption of anode 2. This relationship is explained in more detail by means of FIGS. 2A, 2B and 2C. In each case, means for registering the position of the cathode (also called position sensor 7 below) are arranged on the upper part 4 of the housing. Said position sensor can be a commercially available position sensor.
The relationship between the consumption of the sacrificial anode 2 and the position of the cathode 3 relative to the upper part 4 of the housing is illustrated in three stages in FIGS. 2A-2C.
In FIG. 2A, the situation is presented as in FIG. 1. The sacrificial anode 2 is unused. Consequently, the cathode 3 has taken its highest point in the upper part 4 of the housing. Now, when the thickness of the sacrificial anode 2 decreases due to the continuous operation of the reactor, cathode 3 sinks farther downward and consequently a pin 29 of the position sensor 7 moves downward relative to the upper part 4 of the housing. This situation is shown in FIG. 2B. At this point, the sacrificial anode 2 still has only about half the thickness of the unused state. The position of cathode 3 can be measured from the relative movement of the pin 29 relative to the upper part 4 of the housing and, due to the spacer 9, the thickness of the sacrificial anode 2 can also be determined.
In FIG. 2B, it can easily be seen that the channel 10, which is delimited by the surfaces 25 and 27, likewise moves downward with increasing consumption of anode 2. Consequently, transition regions 31 made in the lower part 1 of the housing both at the inlet 5 and at the outlet 6 must be sufficiently long, mainly in the vertical direction. This ensures that the treated liquid gets into channel 10 and from there reaches outlet 6 independent of the thickness of anode 2.
FIG. 2C shows the state in which the anode 2 has been completely consumed. In this state, the spacers 9 lie directly on the lower part 1 of housing 1 [sic]. Of course, current can no longer flow through the cathode 3. Thus, the complete consumption of anode 2 can also be detected through this decrease of the current to zero. Of course, it is also possible to detect the complete consumption of anode 2 by detecting the position of the output signal of the position sensor 7.
According to the invention, it is possible to operate a plurality of reactors according to the invention in series and/or in parallel. This arrangement is shown schematically in FIG. 3.
It is possible here that, in each case according to the consumption of anode 2, not all of the reactors will be supplied with electric voltage. Rather, there is the possibility of providing only a part of the reactors with electric power in correspondence with the amount of accruing liquid that must be treated.
When a plurality of parallel lines of reactors are present, it is also possible to hydraulically uncouple a reactor or a line of reactors from the system and then to replace at least one anode in the reactor or idle line. The operation, or the treatment of the liquid, can then be continued in the parallel connected reactors or lines of reactors without interruption.
In FIG. 3, the reference numbers mean:
119 Inlet
120 Outlet
121 Sensor for measurement of phosphate content in outflow
122 Control
123 Power supply of a reactor
124 Output signal of position sensor 7
125 Output signal of sensor 121
126 Control signal of control 122 for the performance (voltage U and/or current I) of a power supply 123
127 Output performance of a power supply 123
It becomes clear from this presentation that the performance of the overall system is scalable in a very wide range by connecting and disconnecting individual reactors or lines and, because of the redundancy of the parallel and series connected reactors, the overall system can be operated very reliably.

Claims

1. A reactor comprising a housing (1, 4), a cathode (3), and an anode (2), wherein the cathode (3) and the anode (2) delimit a channel (10), the cathode (3) being movable in the housing (4) relative to the anode (2).

2. A reactor as in claim 1, wherein the anode is a sacrificial anode and a spacing (S) is included between surfaces (25, 27) of the anode (2) and the cathode (3) delimiting the channel (10), independent of consumption of the anode (2).

3. A reactor as in claim 1, wherein at least one electrically nonconductive spacer (9) is disposed between surfaces (25, 27) of the anode (2) and the cathode (3) that delimit the channel (10).

4. A reactor as in claim 3, wherein the spacing (S) is kept constant with the help of gravity, one or more springs, or one or more actuators.

5. A reactor as in claim 2, wherein the surfaces (25, 27) of the anode (2) and the cathode (3) that delimit the channel (10) are planar.

6. A reactor as in claim 2, wherein at least one of the anode (2) and the cathode (3) is rectangular.

7. A reactor as in claim 1, wherein the housing includes an upper part and a lower part, and wherein the lower part (1) serves as a transport container for the anode (2).

8. A reactor as in claim 7, wherein outer measurements (L, B) of the lower part correspond to the measurements of a standardized transport system.

9. A reactor as in claim 1, wherein a surface (27) of the cathode (3) that delimits the channel (10) or a surface (25) of the anode (2) that delimits the channel (10) has a plurality of flushing nozzles (12).

10. A reactor as in claim 9, wherein the cathode (3) has a distribution chamber (11), and the flushing nozzles (12) are hydraulically linked to the distribution chamber (11).

11. A reactor as in claim 1, further including means (7) for detection of the position of the anode (2) and/or the cathode (3).

12. A reactor as in claim 1, further including means for detection of electrical current (I) that flows between the anode (2) and the cathode (3), or electrical voltage (U) that is applied between the anode (2) and the cathode (3).

13. A reactor as in claim 1, wherein the anode (2) is a sacrificial anode and comprises a magnesium-containing material.

14. A reactor as in claim 1, wherein a liquid containing phosphate salts flows through the channel, and phosphate salts are removed at the anode.

15. A reactor as in claim 3, wherein the surfaces (25, 27) of the anode (2) and the cathode (3) that delimit the channel (10) are planar.

16. A reactor as in claim 5, wherein at least one of the anode (2) and the cathode (3) is rectangular.

17. A reactor as in claim 2, wherein a surface (27) of the cathode (3) that delimits the channel (10) or a surface (25) of the anode (2) that delimits the channel (10) has a plurality of flushing nozzles (12).

18. A reactor as in claim 3, wherein a surface (27) of the cathode (3) that delimits the channel (10) or a surface (25) of the anode (2) that delimits the channel (10) has a plurality of flushing nozzles (12).

19. A reactor as in claim 5, wherein a surface (27) of the cathode (3) that delimits the channel (10) or a surface (25) of the anode (2) that delimits the channel (10) has a plurality of flushing nozzles (12).

20. A reactor as in claim 2, further including means for detection of electrical current (I) that flows between the anode (2) and the cathode (3), or electrical voltage (U) that is applied between the anode (2) and the cathode (3).